1. Field of the Invention
The invention relates in general to an optical disc drive, and more particularly to a method for controlling laser power of an optical disc drive which uses a circuit laser power curve of one loop circuit to obtain a circuit laser power curve of the other loop circuit.
2. Description of the Related Art
In order to speed up reading/writing data of an optical disc, the optical disc drive, after the optical disc is positioned, would normally use a laser beam of suitable power to recognize disc specification and test laser power under an open-loop circuit or closed-loop circuit control system so as to set up best parameters for the required signal processing and servo system to correctly read/write data of the optical disc.
As indicated in FIG. 1, a power-controlling curve of a conventional optical disc drive is shown. The open-loop circuit and the closed-loop control circuit of the conventional optical disc drive are different circuits and have different levels of signal reference. In order to correctly control the laser power, in the area of the optical disc, the laser powers (such as the powers P1˜P5) outputted from the laser diode are tested by different input voltages (such as voltages V1˜V5) or input currents in a real test. Then, a laser power curve of open-loop circuit or closed-loop circuit is obtained by linear fitting these test points according to a mathematical algorithm. Then, the laser power curve is used as parameters by which the open-loop circuit and the closed-loop circuit of the optical disc drive control the laser diode and output a light beam with correct laser power.
In order to obtain a laser power curve to control the output of laser power, many test points selected from the open-loop circuit and closed-loop control circuit of the optical disc drive need to be tested and the complicated linear-fitting algorithm needs to be calculated, not only wasting time but also deteriorating the efficiency of the optical disc drive. Thus, the conventional optical disc drive still has many problems to resolve in the control of laser power.